1. Field of the Invention
The present invention relates to the back pressure groove structure of a variable displacement vane pump and particularly relates to the back pressure groove structure of a variable displacement pump intended to smoothly flow back pressure oil in back pressure grooves formed in a side plate and a cover plate, to reduce the noise and vibration of the pump.
2. Description of the Related Art
A pressure balance type vane pump has two pairs of pump suction parts and pump discharge parts, the pump suction parts facing each other and the pump discharge parts facing each other.
A variable displacement vane pump, by contrast, has a structure in which only one pair of a pump suction part and a pump discharge part is provided. Back pressure grooves formed in a side plate and a cover plate for supplying back pressure oil assisting in the ejection of vanes are constructed to correspond to the pair of the pump suction part and the pump discharge part.
That is, as shown in FIG. 11, a semicircular arc-shaped back pressure groove 028a supplying back pressure oil for assisting in the ejection of vanes at a pump suction side and a semicircular arc-shaped back pressure groove 028b supplying back pressure oil for assisting in the ejection of vanes at a pump discharge side are formed in a side plate 05. These semicircular arc-shaped back pressure grooves 028a and 028b communicate with each other by two restrictors 50 provided at both sides, respectively. The back pressure groove 028a communicates with a high pressure side (a pump discharge chamber) through a back pressure-side fluid channel 027. Reference symbol 018b denotes a suction convex groove communicating with the pump suction part and reference symbol 019b denotes a discharge through groove communicating with the pump discharge part.
Also, as shown in FIG. 10, a semicircular arc-shaped back pressure groove 029a supplying back pressure oil for assisting in the ejection of vanes at the pump suction side and a semicircular arc-shaped back pressure groove 029b supplying back pressure oil for assisting in the ejection of vanes at the pump discharge side are formed in a cover plate 03. These semicircular arc-shaped back pressure grooves 029a and 029b do not communicate with each other (see Japanese Patent Application Laid-Open (JP-A) No. 11-93856).
At the pump suction side, as the capacity of the pump chamber increases, vanes are attracted by a cam ring and the ejection rate of vanes increases. To compensate for the increase, the quantity of back pressure oil for assisting in the ejection of vanes tends to be increased. At the pump discharge side, as the capacity of the pump chamber decreases, the vanes are pressed by the cam ring and the ejection rate of the vanes decreases. To compensate for the decrease, the back pressure oil for assisting in the ejection of the vanes tends to be decreased.
Due to this, at the pump discharge side, the back pressure oil forced out of the back pressure groove 029b of the cover plate, back pressure holes 016 (see FIG. 12) of a rotor and the back pressure groove 028b of the side plate is induced to flow into the back pressure groove 028a at the pump suction side through the restrictors 050 and further into the back pressure holes 016 of the rotor at the pump suction side.
Then, as shown in FIG. 12, the back pressure oil which is flowing into the back pressure groove 028a at the pump suction side through the restrictors 050 collides against the back pressure oil fed into the pump suction-side back pressure groove 028a from the high pressure chamber (pump discharge chamber) to compensate for the increase of the ejection rate of the vanes due to the increased capacity of the pump chamber at the pump suction side.
The collision between the back pressure oil forced out of the back pressure groove 028b of the side plate at the pump discharge side and the back pressure oil (high pressure oil) flowing into the back pressure groove 028a of the side plate at the pump suction side may cause the problems of pump noise and pump vibration.
It is an object of the present invention to solve the above-stated problems of the conventional variable displacement vane pump and, in particular, to provide the back pressure groove structure of a variable displacement vane pump capable of realizing the smooth flow of back pressure oil flowing in back pressure grooves formed in a side plate and a cover plate and capable of reducing the noise and vibration of the pump.
A back pressure groove structure of a variable displacement vane pump according to the present invention comprises a rotor rotatably contained in a pump housing and having a plurality of vane grooves arranged radially and equidistantly in a circumferential direction. A cam ring is arranged in the pump housing in a movable and displaceable manner, fitted into the pump housing to form a pump chamber with an outer peripheral portion of the rotor and applied with an urging force to provide a maximum volume of the pump chamber. A side plate is contained in the pump housing in a non-rotatable manner, slidably contacting with one sides of the rotor and the cam ring and having back pressure grooves communicating with the vane grooves. A cover plate is provided, dosing an opening of the pump housing, slidably contacting with other sides of the rotor and the cam ring and having a back pressure groove communicating with the vane grooves, characterized in that the back pressure grooves of the side plate communicate with a high pressure side and are divided back pressure grooves obtained by dividing an annular back pressure groove into a pump suction side groove and a pump discharge side groove. The back pressure groove of the cover plate is an annular back pressure groove.